1. Field of the Invention
This invention relates to stripping tin or tin-lead alloys from copper substrates, and more particularly to new and improved compositions and method for selectively stripping tin or tin-lead alloys from copper substrates.
2. Description of the Prior Art
U.S. Pat. No. 3,677,949 to Brindisi et al discloses and claims acidic solutions for selectively stripping tin or tin-lead alloys from copper substrates. Such solutions are aqueous solutions comprising a nitro-substituted aromatic compound having one or more --NO.sub.2 groups attached to the aromatic ring and a water-solubilizing substituent also attached to the aromatic ring, an inorganic acid capable of reacting with tin and lead to form water-soluble salts thereof, for example a fluorine-containing inorganic acid, e.g. fluoboric acid or fluosilicic acid, a thiourea, e.g. thiourea per se, for preventing re-deposition of stripped tin onto the copper, and as accelerator an acid of the formula RCOOH wherein R is 1-2C alkyl or a hydrogen atom. Although these stripper solutions give good results in stripping or dissolving the tin or tin-lead alloy from the copper substrate without any substantial attack of the copper, the solutions do leave room for improvement from the standpoint of the stripping rate. A desideratum is that the stripper solutions have a faster or more rapid stripping rate without any substantial or significant attack on the copper surface, and while preventing re-deposition of stripped tin onto the copper surface.